Downhole systems may be used to drill, service, or perform other operations on a wellbore in a surface location or a seabed for a variety of exploratory or extraction purposes. For example, a wellbore may be drilled to access valuable subterranean resources, such as liquid and gaseous hydrocarbons and solid minerals, stored in subterranean formations and to extract the resources from the formations.
In some wellbores, a casing may be installed to support the wellbore and to isolate the wellbore from fluids and material from the surrounding formation. In some wellbores, the casing may be removed in preparation for drilling of a lateral borehole from the wellbore, for slot recovery, or for abandonment purposes. In the case of wellbore abandonment, verifying the integrity of a cement plug in a well may be regulated by various jurisdictions to guard against environmental hazards. Such regulations may include verifying the integrity of the cement behind casing and, if the integrity is poor, sectioning of a certain length of casing and using a cement plug that directly contacts the surrounding formation. The casing may be removed by milling the casing from the surface of the wellbore and running a milling tool (e.g., a casing mill) downward through the wellbore. Portions of the casing may also be removed selectively at specific downhole locations by tripping a milling tool (e.g., a section mill) into the wellbore, expanding the section mill in place, and rotating and moving the milling tool axially to remove the desired amount of casing.